1. Field of the Invention
The present invention relates to an improvement in igniters having particular utility in full head-end solid propellant rocket motors.
2. Description of the Prior Art
Conventionally, the igniter for large solid propellant rocket motors is a miniature rocket motor. Such igniters are known in the prior art as "pyrogen" igniters. A pyrogen igniter or ignition system usually is mounted in the forward or head end of the motor through a central bore or hole in the propellant.
Ongoing improvements in solid propellant mechanical properties, grain configurations, and grain analysis methods have made increases possible in volumetric loading efficiencies of solid propellant rocket motors. One grain configuration which maximizes propellant loading efficiency is the head-end web. This propellant grain design, however, having no central bore, prevents the use of conventional head-end ignition systems.
Optimization of high strength, lightweight rocket motor cases and submerged, optimized rocket motor nozzles leave little space for aft-end igniters. A form of igniter proposed in the prior art for this type of rocket motor is the lightweight consumable wafer igniter disclosed in U.S. Pat. No. 4,498,292 issued to C. Max White on Feb. 12, 1985, and assigned to the assignee of the present invention. This wafer igniter is compatible for various motor grain configurations. Under large internal motor free volume conditions, however, igniter combustion instability may occur causing the igniter to become extinguished before ignition of the rocket motor propellant is effected. Such instability stems from an inherent limitation, in a housing of wafer configuration of acceptable weight and bulk, of the pressure at which the gas producing reaction takes place.
Another form of igniter having utility for rocket motors employing head-end web solid propellants is disclosed in U.S. Pat. No. 4,503,773 which was issued on Mar. 12, 1985, to Christopher W. Bolieau and is assigned to the assignee of the present invention. U.S. Pat. No. 4,503,773 discloses a consumable igniter that is especially useful for igniting head-end web solid propellant rocket motors which have a capability of being offloaded to meet specific total impulse requirements. Such offloading is achieved by machining out propellant from the motor. Since the resulting larger free volume makes ignition of the motor more difficult, the igniter is mounted to the propellant grain, specifically in a cavity formed in the aft end surface thereof, in order to position the source of heat for ignition as close as possible to the surface to be ignited. Although not detrimental in rocket motors developed for offloading as described, the use of such a cavity is disadvantageous when it is desired to maximize propellant volumetric loading efficiency.
U.S. Pat. No. 4,530,516 issued to G. V. Adams et al., also assigned to the assignee of the present invention, discloses a housing construction for a gas generator for rapidly filling a vehicle inflatable cushion restraint system comprising stamped mating aluminum shells that are attached to each other by a hollow steel center-tie member that is provided at the center of the housing with the gas generator initiator assembly mounted therein.
A need exists for an inexpensive, lightweight consumable igniter which is operable at pressures higher than possible with wafer igniters and thus is not subject to the aforementioned combustion instability problem under large rocket motor free volume conditions, thereby to enable the use of the improvements that have been made in solid propellant mechanical properties, grain configurations and analysis methods that make possible maximization of propellant loading efficiencies. The present invention was devised to fill the technological gap that has existed in the art in these respects.